Monthly Palmer Drought Index values for the periods 1931–40, 1941–50, 1951–60 and 1961–69 were subjected to eigenvector analysis. Patterns and periods of variable moisture conditions resulted which fit well the patterns found in drought studies of areas east and west of the upper Midwest. The 1930's and 1950's included years of severe drought but the patterns of drought were not identical. The 1930's drought spread from the west; the 1950's drought spread from the south and southwest. The 1940's and 1960's were wetter than normal in the upper Midwest.